Magnesium alloy



Patented July 26, 1938 UNITED STATES MAGNESIUM ALLOY John A. Gann,Midland, Mich, assignor to The Dow Chemical Company, Midland, Mich, acorporation of Michigan No Drawing.

Application November Serial No. 112,289

3 Claims.

been used commercially. In these alloy compositions, however, it is ageneral rule that, when the percentage of alloying constituents has beenincreased sufficiently to give adequate hardness, the brittleness of thealloy is unduly increased, or, in other words, the toughness of thealloy (as expressed by shock or impact resistance) is unduly decreased,thereby impairing the usefulness' of this class of material.

The principal object of this invention is the production of magnesiumalloys having improved combinations of properties, and morespecifically, the production of magnesium alloys having a goodstrength-weight ratio and a good toughness-hardness ratio. Other objectsand advantages will appear as the description proceeds.

This invention is based on the discovery that the above cited objectivesmay be obtained by simultaneously combining all of the metals magnesium,aluminum, tin, and zinc in definite proportions to form the newquaternary alloy product consisting of magnesium, aluminum, tin, andzinc, and that this new alloy may be improved by the addition ofcadmium, thereby giving as a new product a quinary alloy consisting ofthe metals magnesium, aluminum, cadmium, tin, and

zinc.

These new polynary alloys of magnesium-aluminum-tin-zinc andmagnesium-aluminum-tinzinc-cadmium have very good properties in the formof castings. Moreover, such alloys can be heat treated and/or readilyworked, as by rolling, forging, or extrusion, to form articles havingstill better properties. The aluminum content may vary from about 1 to16 per cent, the tin content from about 0.5 per cent to per cent, thezinc content from about 0.5 per cent to 10 per cent, and the cadmiumcontent from about 1 per cent to 10 per cent. The magnesium contentshould,

in general, be not less than approximately 80 per cent when the alloy isto be used for the production of castings and extrusions, and, ingeneral, not less than approximately90 per cent when the alloy is to beused for the production of forgings, sheet, and plate. If the castingsare to be heat treated, I normally prefer to use an alloy containingapproximately 6 per cent to 10 per cent of aluminum, 2 per cent to 6 percent of tin, and 1 per cent to 3 per cent of zinc. When cadmium is usedin this alloy, it should normally be added in amounts of 1 per cent to 5per cent. An alloy composition within the scope of my inblow impacttest. U

vention, which is satisfactory for the production of sheet, consists ofapproximately 2 per cent of aluminum, 1 per cent of tin, 0.75 per centof zinc, .1 per cent of cadmium, the balance being magnesium.

Examples of the new polynary alloys are given in the accompanying tableswhich show their properties as determined on sand cast test specimens,with the properties of the parent ternary alloys given for comparison.In these examples, the parent ternary alloys were produced by theaddition of increasing amounts of aluminum to magnesium-tin alloys, bythe addition of increasing amounts of aluminum to magnesiumzinc alloys,and by the addition of increasing amounts of zinc to magnesium-tinalloys, while the new polynary alloys were obtained by adding increasingpercentages of aluminum to magnesium-tin-zinc alloys or tomagnesium-tin-zinccadmium alloys. Since the specific gravity of thesealloys is approximately constant within the composition range underconsideration, the strength-weight ratios of these alloys areapproximately proportional to their tensile strengths. Toughness valuesare expressed in terms of foot-pounds of energy absorbed on breaking anotched bar specimen in the single- Table 1 gives the tensile strengthdata for the new polynary alloys consisting of magnesium,

2 per cent of tin, 2 per cent of zinc, plus increasing percentages ofaluminum, compared with its parent ternary alloys. The first column oftensile strength data gives the range of values obtained by addingaluminum (or zinc) in amounts varying from 1 per cent to 12 per cent.The second column of tensile strength data gives the correspondingvalues obtained by adding aluminum (or zinc) over the narrower range offrom 4 to 8 per cent. The third column of the tensile strength datagives the values for the alloys containing 2 per cent of aluminum (or ofzinc). Table 11 gives similar data for another series of ternary alloyscompared to my new polynary Table II Similar property improvements,particularly in regard to the toughness-hardness ratio, are liken n wiseobtained with other magnesium-aluminum- Composition g g ggcadmium-tin-zinc alloys as illustrated for' example, in Table V. In thiscase two series of 5 alloys were prepared, namely, by the addition of j$increasing amounts of aluminum toa magnesium Ms+ 181300 alloy containing2 per cent of tin, and 2 per cent of Mg-l-4%Sn+4%Zn+4%Al Q. 26,300 zinc;and by the addition of increasing amounts of aluminum to a magnesiumalloy containing 2 In the ples giv in T bles I a d the per cent ofcadmium, 2 per cent of tin, and 2' w qu a y al a be considered as percent of zinc, thereby increasing the hardness s been produced by theaddition of a fouljth and decreasing the toughness of the alloy. The 7metal to One of the, Parent ternary alloys, W hardness andimpact-toughness values for each 15 g f g g g g z ggf 8: 2 :12 g 2%;;series of alloys were plotted against the percentage of aluminum.Impact-toughness values than the correspondmg ternary alloys Table wereread from these curves corresponding to III, however, shows that thequaternary alloy is Brine hardness Values of 45 50 55 and 60 likewisedistinctly superior to the three parent r ternary alloys when the alloycompositions are respectively. The data n Table Vshow that for 20 soregulated that all compositions contain the a gtven hardness ttmpact'toughness Values I same total percentage of alloyingconstituents. of the cadmtum'bearmg alloys are greater than thecorresponding values of the cadmium-free Table III alloys 25 CompositionTensile strengghitbhlisgg. in. [01' ys Table V Impact-toughness, ft.-lb.Base Added 1m 12% 4:0 8% gg, 3

- metal addedmetal addedmetal metal Brinenhatdness M +27 Mg+2% 30 I 33Mg+8%Sn Al 15,e00-22,20o 1s,90o-22,200 22,200 zn'+ Mg+8%Zn Al 11,800-20, 16, 400-13, 100 18,100 Mg+8%Sn Zn 2o,1oo-21,aoo 2o,soo-21,20021,200 Mg+4%Sn+4%Zn Al 22,1o0 2s,30o 26,300 :5 E

The new magnesium-aluminum-tin-zinc qua- 60 ternary alloys are likewisecharacterized by a good ratio of toughness to hardness. This was My newpolynary alloys, consisting of ma established as follows.Impast-toughness and nesmm a1uminum tin zinc magnesimm 40 hardnesscurves were drawn for numerous series aluminum cadmium tin zinc, may beprepared 9 tentary and polynary alloys Simllar to those by the usualmethods for melting and alloying listed in Tables I through III. Thehardness metals with magnesium such as addm th values corresponding toimpact-toughness values g 8 of 1.5, 2.25, and 3 foot-pounds respectivelywere spefmve alloymg metals to t of molten mag- 45 read from thesecurves; The tabulated data nesium protected from o ndatlon by a cover ofshowed that good and very good toughness-hardfluid ness ratios wereobtained in 31 per cent of the other modes of applymg the Prmclpte of mymagnesium a1un inum ti alloys, in 76 per cent invention may be employedinstead of those exof th magnesium-a1umjnum zinc alloys, and in plained,change being made as regards the in- 5.0" 8 per cent 'of themagnesium-tin-zinc alloys gredients and the steps herein disclosed,provided whereas using the same basis of comparison, 88 those stated byany of the following claims or per cent of my newmagnesium-aluminum-tintheir equivalent be employed. tsing1 aloys showedgood to very good toughness I particularly point out and distinctlyclaim 0 ar HESS ra 10S. as my invention:

I have likewise found that the new magnesium- 1 A magnesium-base alloyconsisting of aluminum-tin-zinc alloys may be improved by theproximately 1 per cent to 16 per cent of a1um1 addition ofcadmium. Thisis illustrated, ior num 05 per cent to 10 per cent of tin a 0.5 exampley the data m Table where gains per cent to 10 per cent of zinc, thebalance being are shown in strength, hardness, and toughness. magnesium.50

Table IV 2. A magnesium-base alloy consisting of approximately 6 percent to 10 per cent of alumi- Composition num, 2 per cent to 6 per centof tin, and 1 per Prioperty cent to 3 per cent of zinc, the balancebeing mag- 5 -Mg+4% Al+ Mg+4% Al+2% Sn+ nes1um.,. 2% Sn+2% Zn 2% +273 Cd3. A magnesium-base alloy consisting of 8 per cent of aluminum, 2 percent of tin, and 2 per cent gg iffiggfg ggf'f gf:. gg of zinc, thebalance being magnesium; Impact toughness, ft.-lb 5. 5 c. 2 70 JOHN A.GANN.

